The present invention relates to a fastener for securing workpieces together and more particularly to a multiple piece fastener including a pin and a collar.
One example of such a fastener can be seen in U.S. Pat. No. 4,846,611, "Fastener System and Fastener for Shipping Containers and the Like" issued to Sadri et al., assigned to the same assignee as the present invention and incorporated herein by reference. This patent discloses an elongated pin having a head portion and a shank portion. The shank portion includes a set of helical splines to engage a bore in a tubular collar. As the collar is pressed onto the pin, the splines flow the collar material into grooves associated with the splines to provide an interference engagement between the two. To keep the splines from significantly expanding the collar radially as it is pressed onto the pin, the degree of interference between the splines and the bore and the relative hardness of the pin to the collar are controlled. In the disclosed preferred embodiment, the pin has been heat-treated and has a hardness of approximately two times the hardness of the collar.
Another example of such a fastener can be seen in U.S. Pat. No. 4,627,775, "Blind Fastener with Grip Compensating Means", issued to Dixon, assigned to the same assignee as the present invention and incorporated herein by reference. This patent discloses a blind fastener including an elongated pin and a tubular collar. The pin includes a single forming or extruding land having a diameter that is larger than an inner diameter of the collar. As the collar is pressed onto the pin, the extruding portion extrudes a portion of the collar material into a lock groove associated with the extruding land to lock the collar to the pin. This operation also results in the radial expansion of the collar due to the force from the extruding land. In one embodiment disclosed, the pin has been heat-treated to a hardness of R.sub.c 48-52.